Manufacturers continue to develop replacement binder formulations to replace the traditional phenol-formaldehye and urea-formaldehye binders that have been used for decades. Formaldehyde is considered a probable human carcinogen, as well as an irritant and allergen, and its use is increasingly restricted in building products, textiles, upholstery, and other materials. In response, formaldehyde-free binder systems are being developed and commercialized.
The first generation of replacement binder systems included polycarboxylic acid formulations that polymerized polycarboxylic acids and alcohols. The polymerization reaction involved the esterification of the carboxylic acid groups on the polycarboxylic acids and the hydroxyl groups on the alcohols, which generated environmentally benign water as the main polymerization byproduct. However, the high concentrations of polycarboxylic acids in these binder formulations make them very acidic and create corrosion problems for the manufacturing equipment used to make fiberglass insulation and fiber-reinforced composites.
The first generation of replacement binders also tend to rely heavily on non-renewable, petroleum-based starting compounds. Increasing worldwide demand for fossil fuels has driven up the costs of these materials and created both economic and environment concerns about the sustainability of these binder systems. Thus, manufacturers have been developing a new generation of replacement binder formulations that reduce or eliminate petroleum-derived starting materials.
One promising new class of binder systems rely on carbohydrates as a sustainable, environmentally benign replacement for the petroleum-based starting compounds. Carbohydrate-based binder systems typically polymerize reducing sugar carbohydrates with a crosslinking compound to produce an effective binder for fiberglass insulation and other products. The polymerization process converts the water soluble carbohydrates into water insoluble polymers with good moisture resistance and aging characteristics.
Carbohydrate binder formulations normally start as aqueous solutions that are saturated with the starting carbohydrates. The formulations may also include polymerization catalysts that are often metallic ammonium salts of simple inorganic acids. Unfortunately, the high concentrations of carbohydrates in the aqueous binder solution substantially reduce its capacity for dissolving these salts. The poor solubility of the catalyst is compounded by the ions that commonly contaminate the industrial/municipal sources of water used in the binder solution. Between the multivalent ions that naturally contaminate the water source and the additional ions added by the catalyst, the binder solution often becomes oversaturated and precipitate out a quantity of the salts. As these salt precipitates build up in the equipment that transports the binder solution, they can cause frequent and costly maintenance shutdowns.
One way to reduce these shutdowns is to decontaminate the supply of water used to make the binder formulations. These decontamination techniques include running the water through ion exchange columns that replace a portion of the multivalent ions with monovalent ions such as sodium (Na+) or potassium (K+) ions. This process is sometimes referred to colloquially as water softening, and the ion exchange equipment as a water softener. Unfortunately, the ion exchange columns need frequent and costly recharging to reduce the multivalent ion concentrations to the levels needed, which has a significant effect on maintenance shutdowns and makes this approach impractical for most manufacturing applications. In addition, the addition of extra sodium ions can have an adverse effect on cure rate and water resistance in the cured binder. Thus, there remains a need to address the salt precipitation problems with carbohydrate binder solutions, and this and other problems addressed in the present application.